1. Field of the Invention
The present invention relates to a phosphor which emits a visible light upon excitation by an ultraviolet ray, a visible light, or an electron beam and has a β-type Si3N4 crystal structure, wherein the luminescence peak has a small half-value width and a sharp peak shape, a manufacturing method of the phosphor, and a luminescence device utilizing the phosphor.
2. Background Art
The phosphor is utilized in a fluorescent display tube (VFD: vacuum-fluorescent display), a field emission display (FED: Field Emission Display) or SED (Surface-Conduction Electron-Emitter Display), a plasma display panel (PDP: Plasma Display Panel), a cathode-ray tube (CRT: Cathode-Ray Tube), a white light-emitting diode (LED: Light-Emitting Diode), and so on. In any of these applications, it is necessary to provide the phosphor with energy to excite the phosphor in order to have the phosphor emit the fluorescence and the phosphor is excited by an excitation source with high energy such as a vacuum ultraviolet ray, an ultraviolet ray, an electron beam, and a blue light so as to emit a visible light ray. However, the phosphor is exposed to such excitation source that the luminance of the phosphor tends to deteriorate and lower the degree of the brightness. Therefore, the phosphor having little degradation in the brightness is desired. Therefore, a sialon phosphor is proposed as a phosphor having little degradation in the brightness instead for the conventional phosphor such as silicate phosphor, phosphate phosphor, aluminate phosphor, sulfide phosphor, and so on.
As an example of this sialon phosphor is manufactured in the following manufacturing process as generally described below. First, silicon nitride (Si3N4), aluminum nitride (AlN), europium oxide (Eu2O3) are mixed with predetermined respective molar ratios and the resultant mixture is fired by a hot press method in one atmospheric pressure (0.1 MPa) of nitrogen atmosphere at 1700° C. for one hour (for example, refer to Patent reference 1). It is reported that α-sialon activated with Eu ion manufactured in the above process became a phosphor to emit a yellow light of wavelength range of 550 nm to 600 nm when it was excited by the blue light having a wavelength range of 450 to 500 nm.
Further, a blue phosphor activated by Ce having a host crystal of JEM phase (LaAl(Si6-zAlz)N10-zOz) (refer to Patent reference 2), a blue phosphor activated by Ce having a host crystal of La3Si8N11O4 (refer to Patent reference 3), and a red phosphor activated by Eu having a host crystal of CaAlSiN3 (refer to Patent reference 4) are known.
As another sialon phosphor, a phosphor of β-type sialon doped with a rare earth element is also known (refer to Patent reference 5) and it is shown that phosphors activated by Tb, Yb, and Ag are those which emit a green light of 525 nm to 545 nm. However, a phosphor having a high emission intensity has not been obtained since the activation elements are not well incorporated in the host crystal as a solid solution, but reside in the boundary phase because the synthesis temperature is so low as 1500° C.
As a sialon phosphor to emit fluorescence of high brightness, β-type sialon phosphor doped with divalent Eu is also known (refer to Patent reference 6) and it is shown that it becomes a green phosphor.    [Patent Document 1] Specification of Japanese Patent No. 3,668,770    [Patent Document 2] WO 2005/019376    [Patent Document 3] Japanese Patent Application Publication No. 2005-112922    [Patent Document 4] WO 2005/052087    [Patent Document 5] Japanese Patent Application Publication No. S60-206889    [Patent Document 6] Japanese Patent Application Publication No. 2005-255895
In the application of a backlight for a liquid crystal display, only three colors: red, green, and blue are necessary, but other color elements are not necessary. Therefore, only three kinds of phosphors having sharp spectra of red, green, and blue are necessary for this application. It is hardly possible to find, in particular, a green phosphor to emit luminescence which exhibits a sharp peak and high color purity. The green phosphor of β-type sialon described in Patent reference 6 exhibits a relatively wide spectrum so that it is hardly to say the sharpness is enough.